Intravenous bolus nitroglycerin--hemodynamic effects and clinical implications

Intravenous bolus nitroglycerin has been used routinely in our cardiac catheterization laboratory during the past three years. Observations on more than 1500 patients suggest that in the supine properly hydrated patient intravenous nitroglycerin produces an initial rapid fall in arterial pressure (systolic, diastolic, and mean). This is followed by gradual return of arterial pressure toward but not to baseline during the subsequent 30-60 seconds. There is a concomitant fall in left ventricular end-diastolic pressure (LVEDP), which appears to be biphasic. Initially, LVEDP falls concomitantly with aortic pressure; subsequently, there is further decrease in LVEDP at a time when aortic pressure is nearly back to baseline. These observations suggest that bolus nitroglycerin, as opposed to continuous nitroglycerin infusion, may act primarily on resistance vessels (systemic arteries), and secondarily on capacitance vessels (systemic veins). A series of experiments was designed to test this hypothesis. During routine right and left heart catheterization of patients with suspected coronary artery intravenous bolus nitroglycerin (.1 mg-.8 mg) was injected into inferior vena cava, pulmonary artery, left ventricle, aortic root, distal aorta, and coronary aorta. The time course of bolus nitroglycerin effect on central venous pressure, pulmonary artery pressure, left ventricular end-diastolic pressure, and arterial pressure was observed for the various injection sites. These time courses of effect were compared to appearance times of indocyanine green injected into the various injection sites, and sampled from the various measuring sites. Initial data suggest that the initial rapid fall in blood pressure is secondary to a primary decrease in systemic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)